1. Field of the Invention
The present invention relates to an overheat detection circuit, an overheat protection circuit including the overheat detection circuit, and a semiconductor device including the overheat protection circuit.
2. Description of the Related Art
FIG. 6 is a circuit diagram for illustrating a related-art overheat detection circuit 600.
The related-art overheat detection circuit 600 is configured in the following manner.
A constant current source 608 is connected between a power supply terminal 60 and an anode of a diode 601, to thereby output a constant current JO.
A cathode of the diode 601 is connected to one end of an adjustable resistor 613, and another end of the adjustable resistor 613 is connected to a ground terminal 61. The anode of the diode 601 is connected to a gate of a P-channel transistor 611. A source of the P-channel transistor 611 is connected to the power supply terminal 60 and a drain thereof is connected to an output terminal 62.
Resistors 609 and 610 are connected in series between the power supply terminal 60 and the ground terminal 61. A gate of an N-channel transistor 612 is connected to a node between the resistor 609 and the resistor 610. A drain of the N-channel transistor 612 and a source thereof are connected to the output terminal 62 and the ground terminal 61, respectively.
When temperature increases, an absolute value of a threshold voltage (Vth) of the P-channel transistor 611 decreases. Meanwhile, a voltage at an anode terminal of the diode 601 decreases. That is, a difference between a voltage at a gate terminal of the P-channel transistor 611 and a voltage at the power supply terminal 60 increases.
Therefore, when temperature increases, the threshold voltage (Vth) of the P-channel transistor 611 and the difference between the voltage at the gate terminal of the P-channel transistor 611 and the voltage at the power supply terminal 60 reverse, to thereby turn on the P-channel transistor 611 and invert a voltage at the output terminal 62 from an electric potential at the ground terminal 61 to an electric potential at the power supply terminal 60.
In this way, the related-art overheat detection circuit 600 is configured to detect a state of overheating based on change in voltage at the output terminal 62 (for example, see Japanese Patent No. 4920305).
However, in order to adjust a detection temperature of the overheat detection circuit with the related art, a resistance value of the adjustable resistor 613 needs to be adjusted in consideration of a threshold voltage of the P-channel transistor 611, temperature characteristics of the threshold voltage of the P-channel transistor 611, a value of an output current I0 of the constant current source 608, temperature characteristics of the constant current source 608, and temperature characteristics of the adjustable resistor 613. The threshold value and the resistance value of the transistor, and the constant current each vary due to process variation, and thus, all of those variations need to be taken into consideration. This has made such adjustment extremely difficult.